Water-swellable clays that have acceptable water-swellability and colloidal properties, e.g., the non-blue bentonites having a Fe.sup.+3 /Fe.sup.+2 ratio above 1.0, and preferably above 3.0, have a great number of industrial uses that rely upon the ability of the clay to absorb many times its weight in water, to provide a gel structure of sufficient strength to hold solids in suspension, and the ability of the water-swellable clays to act as a binder in forming sand molds in the metal casting industry and in pelletizing finely divided ores, e.g., iron ores, such as taconite. Some bentonite clays, such as the blue bentonites disclosed in Clem U.S. Pat. No. 2,672,442, require the uptake of calcium ions to provide acceptable water swellability and colloidal properties for industrial acceptance. The water-swellable clays useful as starting materials in accordance with the present invention are non-blue bentonites (green to greenish yellow to yellow to cream colored) that have industrially acceptable water swellability and colloidal properties and have a Fe.sup.+3 /Fe.sup.+2 ratio greater than 1.0, preferably at least 3.0, and most preferably in the range of about 5.0 to about 15.0. Some of the industrial uses for these non-blue bentonites are generally described below.
1. Drilling Muds
In drilling wells by rotary methods it is a common practice to circulate, continuously, a drilling mud or fluid into and out of the borehole during the drilling operation. The drilling mud is pumped into the drill pipe from a mud pit and the mud passes down to the bottom of the borehole. The drilling mud then flows upwardly through the annular space between the borehole wall and the drill pipe, and finally flows from the borehole through a mud ditch back to the mud pit, wherein the mud is mechanically or chemically treated before recirculation through the borehole.
The drilling mud serves several purposes that influence such factors as the drilling rate, cost, efficiency and safety of the operation. The drilling mud lubricates and cools the drill bit, acts as a vehicle to carry the cuttings from the borehole, and provides sufficient equalizing hydrostatic pressure against the formation wall to prevent the borehole wall from cave-in during drilling. By using proper mud formulations, the borehole entry of gases and fluids encountered in the formations pierced by the drill is inhibited, thereby preventing possible collapse or blowouts resulting from uncontrolled influxes of these formation fluids. The drilling mud also exerts a "wall-building" effect whereby it often forms a thin filter cake on a borehole wall, thus sealing off the borehole and reducing water loss to the penetrated formations.
An acceptable mud must have body, yet be free-flowing with relatively low viscosity in order to facilitate pumping. The mud must also have an acceptable gel strength in order to suspend solid material, if circulation is interrupted, and to prevent accumulation of solids at the drill bit to avoid mechanical jamming. Acceptable drilling muds may be either oil-based or water-based, and they are normally treated to provide the rheological properties that make them particularly desirable and useful for drilling wells. For example, drilling muds may be treated with barium sulfate (barite) or lead sulfide (galena) to increase their density.
The efficiency of the drilling process is related to the velocity of the mud flowing up the annular space between the borehole wall and the drill pipe. This velocity is in turn related to the viscosity, density and flow properties of the mud. In addition, the drilling mud viscosity is known to depend upon the quality, concentration and state of dispersion of the colloidal solids of the mud. As the drilling operation proceeds, the rheological properties of the mud may be adversely affected by such factors as the nature of the drilled strata, loss or gain of water to the mud, chemically-active contaminants that may flocculate the mud, mud pH, and most importantly, the increasing temperatures and pressures encountered at deeper drilling depths. In order to maintain workable viscosities, the muds must be formulated to respond to varying circumstances and conditions encountered during use. Since improvements in efficiency are realized as the viscosity and density of a mud are increased, it is desirable to optimize drilling mud formulations to possess the highest viscosity and density workably feasible for a given formation at a given depth.
Whenever possible, usually for reasons of economy, water-based drilling muds are used throughout the drilling operation. The suspending solids in water-based drilling muds are typically clays from the kaolinite, montmorillonite or ilite groups. These clays impart desirable thixotropic properties to the drilling mud and also coat the walls of the well with a relatively impermeable sheath, commonly called a "filter cake", that retards fluid loss from the well into the formations penetrated by the well.
An exemplary montmorillonite clay that can be used in a water-based drilling mud is non-blue bentonite. The bentonite is dispersed within the water-based liquid as colloidal particles and imparts various degrees of thixotropy to the drilling mud. Non-blue, e.g., sodium bentonite, water swellable clays, that are re-wetted and re-dried, in accordance with the present invention are initially non-blue clays, e.g., are initially industrially acceptable for this purpose, having good water swellability and colloidal properties and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2, at least above 1.0, preferably at least 3.0 and most preferably in the range of about 5.0 to about 15.0, and, after processing, have excellent rheological properties for use in preparing aqueous drilling muds.
2. Lost Circulation Fluid
One difficulty often encountered in rotary drilling operations involves the loss of unacceptably large amounts of the drilling mud into a porous or cracked formation penetrated by the drill. The loss of drilling mud is termed "lost circulation", and the formation is termed a "lost circulation zone" or a "thief formation".
Lost circulation occurs when the well encounters a formation either having unusually high permeability or having naturally occurring fractures, fissures, porous sand formations, cracked or cavernous formations and other types of strata characterized by crevices, channels or similar types of openings conducive to drilling fluid loss. In addition, it is also possible for a formation to be fractured by the hydrostatic pressure of the drilling mud, particularly when a changeover is made to a relatively heavy mud in order to control high internal formation pressures.
When lost circulation occurs, the drilling mud pumped into the well through the drill string enters the cracks in a cracked formation or the interstices of a porous formation and escapes from the wellbore, therefore precluding return of the drilling mud to the surface. In the most severe situation, the lost circulation zone takes the drilling mud as fast as it is pumped into the wellbore, and, in less severe situations, circulation of the drilling mud can be greatly reduced, and eventually result in a shutdown of drilling operations. Normally, the maximum amount of drilling mud loss that is tolerated before changing programs is approximately one barrel per hour. If a greater amount of drilling mud is lost, corrective measures are needed. Drilling generally is not resumed until the thief formation is closed off and circulation of the drilling mud reestablished.
The interruption of normal circulation prevents the entrainment of cuttings and other materials from the borehole, leads to reduced hydrostatic pressure, possibly followed by the influx into the wellbore of high pressure formation fluids, and can result in the flooding of oil-producing zones with mud or the like, and may eventually cause the drill string to become stuck in the borehole. Even in situations where circulation is not completely lost and some drilling mud can return to the surface, the drilling mud flowing into the lost circulation zone must be replaced continuously. If the drilling mud loss is sufficiently high, the cost of continued drilling or well operation may become prohibitive. Therefore, the lost circulation of drilling mud is a condition that must be prevented or be corrected as quickly as possible.
The best method of controlling lost circulation is to conduct a drilling program such that mud loss will not occur. However, situations exist wherein even correct drilling techniques cannot avoid lost circulation. Therefore, many methods have been used in attempts to plug the cracks or interstices of lost circulation zones to prevent the escape of drilling muds. As a result, a wide variety of materials have been pumped into the well with the drilling mud in an effort to bridge or fill the cracks or interstices of thief formations. It has been found that some materials are successful under certain drilling conditions, yet the same material is unsuccessful under other drilling conditions.
One common method is to increase the viscosity of the drilling mud or to increase the resistance of the drilling mud to flow into the formation. Another technique involves the addition of a bulk material, such as cottonseed hulls, cork, sawdust, perlite, ground walnut shells, hay, wood shavings, granular plastic, vermiculite, rock, mica flakes, leather strips, beans, peas, rice, sponges, feathers, manure, fish scales, corn cobs, glass fiber, asphalt, ground tires, burlap or other fabrics to the drilling mud. By adding these fibrous, flaky or granular solids to the drilling mud and pumping the resulting mixture into the borehole, a bridge or mat forms over the cracks or interstices responsible for drilling mud escape.
Although lost circulation zones frequently are plugged by such bulk materials, successful plugging of the thief formation is not assured. Even if large volumes of a solids-containing drilling mud are pumped into the borehole, a bridge or mat may never form over the cracks or interstices of the thief formation. Moreover, the introduction of large quantities of a drilling mud containing a relatively high percentage of bulky solids can produce pressure surges that cause further fracturing and therefore result in additional fissures for even greater drilling mud losses. Bulk materials further proved unsuccessful in sealing off porous formations because they have a tendency to deteriorate under the high drilling pressures, and therefore decrease in volume and become slimy so as to "worm" into the formation openings without forming an effective seal.
The water-swellable clays processed in accordance with the present invention are processed by starting with an industrially acceptable, e.g., non-blue bentonite clay, that is initially industrially acceptable for this purpose, having good water swellability and colloidal properties and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2 above 1.0, preferably at least 3.0 and most preferably in the range of about 5.0 to about 15.0. The non-blue bentonite clay is re-wetted and re-dried, as described in more detail hereinafter and, after processing, have the ability to continue to swell and increase viscosity upon entering the interstices of a thief formation for , effective plugging.
3. Foundry Industry Binders
Green sand molding is the production of molded metal objects from tempered molding sand and is the most diversified molding process used to cast ferrous as well as non-ferrous metal castings. Green sand molding is favored by foundry men because it is economical and permits both quality and quantity production. Green sand is defined as a water tempered molding sand mixture with plasticity. A green sand mold used for casting steel usually consists of silica sand, a clay binder, and/or an organic additive mulled together with temper water.
One or more binders mixed with the silica sand are essential to maintain the sand in a predetermined mold configuration. One of the most commonly employed green sand binders is clay, such as a water-swellable sodium bentonite clay or a low-swellable calcium bentonite clay. The amount of the clay binder that is used together with the sand generally depends upon the particular type of sand used in the mixture and the temperature of firing. Silica sand grains expand upon heating. When the grains are too close, the molding sand moves and expands causing the castings to show defects such as "buckles" (a deformity in the casting resulting from excessive sand expansion), "rat tails" (a rough, irregular depression that appears on the surface of a casting, or a minor buckle), and "scabs" (a breaking away of a portion of the molding sand when hot metal enters the mold). To overcome this harmful expansion, more clay is added to the sand mixture since the clay contracts upon firing thereby compensating for the expansion of the silica sand grains. In green sand molding, the reproducibility of the dimensions obtained on the casting are the result of such factors as shrinkage, changes in dimensions of mold cavity, hardness of mold, stability of molding sand, mechanical alignment of flask and maintaining a fixed temperature.
Clays have been blended in the past in an attempt to achieve acceptable combinations of premeabilities, green compression strengths and dry compression strengths in the molding sand mixture or composition. Toward this end, it is known to mix a sodium bentonite with a calcium bentonite or a kaolinite clay in an attempt to achieve the high dry compression strength of the sodium bentonite clay together with the high green compression strengths of the calcium bentonite clay and the low permeability of the kaolinite clay. See Foundry Sand Practice by Clyde A. Sanders, 6th Edition, 1973, pp. 585-590. As set forth in a co-pending application Ser. No. 336,095, filed Apr. 11, 1989, hereby incorporated by reference, a mixture of sodium bentonites as a binder in the preparation of a foundry sand provides synergistic results with respect to green compressive strength; hot compressive strength; dry compressive strength; flowability; surface finish; activation speed; and/or shake-out. One or more of these properties are better in the blend than each of the sodium bentonites, prior to blending.
It has been found that by processing water-swellable, e.g., bentonite, clays by re-wetting and re-drying, in accordance with the present invention, by starting with non-blue, e.g., initially industrially acceptable water-swellable clays having good water swellability and colloidal properties and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2 above 1.0, preferably at least 3.0 and most preferably in the range of about 5.0 to about 15.0, after processing, by re-wetting and redrying, such clays have improved foundry properties for use as binders in the foundry industry, when used alone or in combination with other water-swellable clays.
4. Iron Ore Pelletizing
Taconite is a high-grade iron ore that consists chiefly of fine-grained silica mixed with magnetite and hematite. As the richer iron ores approach exhaustion in the United States, taconite becomes more important as a source or iron. To recover the ore mineral in a usable form for the production of iron, taconite must be finely ground, and the magnetite or hematite is concentrated by a magnetic or other process. The concentrate must be agglomerated into chunks of size and strength suitable for the blast furnace.
Industrially acceptable, non-blue, water-swellable clays, particularly sodium bentonites, have been used as binders for iron ores, such as taconite ores, in the formation of pellets having sufficient strength for subsequent processing of the iron ore pellets. Some of the important characteristics for the iron ore pellets bound with water-swellable clay are: ballability, the balling characteristics (kinetics) of the ore-water-clay mixture; wet compression strength of the pellet; resistance to fracture by impact (drop test); deformation under load; resistance to over-wetting of the pellet surface by recondensation of moisture onto the green balls in colder layers during drying; resistance to decrepitation (shock temperature), i.e. sudden pellet-spalling occurring when pellets are heated too rapidly; and dry compression strength.
Green ball agglomerates are normally produced by rolling fine ore in drums, discs or cones. Through the rolling action in the drum, the ore particles are rearranged and come into contact, with each other. At the point of contact, the liquid layers around the particles coalesce, causing a reduction of the external surface of the water film. A decrease in the free surface energy of the agglomerate is the driving force for the formation of the nuclei. During the subsequent growth, these aggregates are compacted. The porosity decreases and the pore-water is forced to the surface. In this so-called transition region, the rate of growth is maximal. Investigations into the mechanism of pellet formation have demonstrated that the kinetics of green pellet formation are extremely dependent on the free moisture content of the system.
Each system, dependent on ore and the water-swellable clay, has critical moisture limits within which strong green pellets are formed. At low moisture contents, the rate of pellet growth is slow and the pellets are brittle. The rate of pellet growth increases as the amount of moisture increases. Beyond this moisture limit, the rate of growth becomes excessive, and the pellets produced are irregular, weak and too plastic. Therefore, there exists a narrow range in which optimum pelletization results are achieved.
Since it is virtually impossible to extract water from the system, it is imperative that the binding additive must have moisture binding ability in order to control the effect of moisture in the feed. Bentonite, the most common additive, makes less water available to participate in the pelletizing process, due to an intracrystalline absorption.
The starting water-swellable clays that are processed in accordance with the present invention, by re-wetting and re-drying, are non-blue, e.g., are initially industrially acceptable for this purpose, having good water swellability and colloidal properties and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2 above 1.0, preferably at least 3.0 and most preferably in the range of about 5.0 to about 15.0, and, after processing, have new and unexpected properties in pelletizing iron ores, particularly taconite.
5. Water Absorbency and Swellability
The water-swellable clays re-wetted and re-dried in accordance with the principals of the present invention are capable of new and unexpected water-absorbency and swellability making them very useful for a number of industrial products and processes. The water-swellable clays re-wetted and re-dried in accordance with the principles of the present invention provide unexpected water absorbency and swellability making the clays very suitable for use in moisture impervious panels; for preventing water contaminated with industrial waste from seeping through soil containing one or more of the treated water-swellable clays; for water-proofing compositions in non-viscous sprayable forms, or paste or putty-like forms, capable of being applied by spray methods, caulking gun, or trowel; for use together with elastomers and/or plasticisers for preventing the seepage of water through the compositions; together with other additives such as xanthan gum and/or other gums for maintaining stability in salt-contaminated water; together with other components to manufacture a flexible grout composition; for use as a water-swellable material in a layered water-sealing article of manufacture; for use in filtering contaminants from oils; for use in clarifying aqueous solutions, such as in the wine industry, and to flocculate contaminants from waste water; and for use in carbonless copy paper when acid treated.
Examples of these technologies and uses for water-swellable clays are disclosed in the following U.S. Patents, all of which are hereby incorporated by reference: Clem U.S. Pat. No. 3,186,896; Clem U.S. Pat. No. 4,048,373; Clem U.S. Pat. No. 4,021,402; Clem U.S. Pat. No. 4,084,382; Clem U.S. Pat. No. 4,087,365; Clem U.S. Pat. No. 4,279,547; McGroarty U.S. Pat. No. 4,316,833; Piepho U.S. Pat. No. 4,332,693; Harriett U.S. Pat. No. 4,534,925; Harriett U.S. Pat. No. 4,534,926; Alexander U.S. Pat. No. 4,634,538; Harriett Pat. No. 4,668,724; Harriett Pat. No. 4,696,698; Harriett Pat. No. 4,696,699; Alexander Pat. No. 4,886,550; Harriett Pat. No. 4,733,989; Alexander Pat. No. 4,832,793; Harriett Pat. No. 4,810,573; and Alexander Pat. No. 4,847,226.
Excellent gel strength is achieved when industrially acceptable, water swellable, non-blue starting clays are processed in accordance with the present invention. The water-swellable clays processed in accordance with the present invention are non-blue, e.g., are initially industrially acceptable for gel strength, having good water swellability and colloidal properties and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2 above 1.0, preferably at least 3.0 and most preferably in the range of about 5.0 to about 15.0, and after processing by re-wetting and re-drying, the clays are excellent suspending agents for use in the cosmetics and pharmaceutical industries in amounts well known in the art.